Cathode ray tube with mutually intersecting focusing coils

ABSTRACT

A cathode ray tube comprising an envelope, a target disposed at the front of the envelope, an electron gun emitting electron beams toward the target, a deflecting coil and a focusing device comprised of a pair of mutually intersecting focusing coils positioned between the target and deflecting coil, the focusing device providing an electromagnetic field acting in the same direction as that in which the electron beams are deflected so as to focus them.

ilnited States Patent 'isuneta ct a1.

[ 1 Dec. 19, 1972 CATHODE RAY TUBE WITH MUTUALLY INTERSECTING FOCUSINGCOILS Inventors: Asahide Tsuneta, Kawasaki; Norio Han-a0, Yokohama, bothof Japan Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Filed:on. 23, 1970 Appl. No: 83,507

Assignee:

Foreign Application Priority Data Oct. 28, 1969 Japan ..44/85716 [1.8.Ci. ..315/27 G11), 313/84, 313/92 LF, 315/31 R Int. Cl ..H0lj 29/66Field of Search ..315/31 R, 27, 31 TV, 22; 313/84, 92 LF [56] ReferencesCited UNITED STATES PATENTS 3,084,276 4/1963 Severin ..315/27 R3,449,621 6/1969 Himmelbauer et al ..315/27 R X 3,585,432 6/1971 Oberg..313/92 LF 2,898,509 8/1959 Clay et al 315/27 R X 3,316,433 4/1967Reiches et al ..315/27 XY Primary Examiner-Carl D. Quarforth AssistantExaminer-E. E. Lehmann Attorney-Flynn & Frishauf [57 ABSTRACT A cathoderay tube comprising an envelope, a target disposed at the front of theenvelope, an electron gun emitting electron beams toward the target, adeflecting coil and a focusing device comprised of a pair of mutuallyintersecting focusing coils positioned between the target and deflectingcoil, the focusing device providing an electromagnetic field acting inthe same direction as that in which the electron beams are deflected soas to focus them.

5 Claims, 5 Drawing Figures PATENTED use 19 I972 SHEET 1 [1F 2 FIG.

PRIOR ART PATENTED DEC 1 9 i972 SHEET 2 UF 2 FIG. 3

FIG. 4

TiME

FlG. 5

EATIIODE RAY TUBE WITH MUTUALLY TNTERSECTING FOCUSING COILS BACKGROUNDOF THE INVENTION The present invention relates to a cathode ray tube. Inthe conventional optical fiber type cathode ray tube, for example, theenvelope 11 assumes a funnel shape having a conical portion 12 and aneck portion 13. At the end of the conical portion 12 of the envelope 11is positioned a target 16 having a fluorescent layer formed on one sideof its fiber plate 14 with said fluorescent layer turned inside. In theneck portion is received an electron gun 17 which consists of a cathodeelectrode 18, first and second grid electrodes 19 and 20 coaxiallyarranged in turn therefrom toward the target 16 and an anode electrode21. Electron beams 22 emitted from the cathode electrode 18 of theelectron gun 17 pass through the opening of the first grid electrode 19,are focused at a crossover point 23 by an electron lens system disposedbetween the first and second grid electrodes 19 and 20 and thenscattered toward the target 16. The scattered electron beams 22 areagain focused on the fluorescent surface 15 by a focusing coil 24 placedon the outer periphery of the neck portion ahead of the electron gun 17.Before reaching the fluorescent surface 15, the electron beams 22 aredeflected by a deflecting coil 25 so as to scan the fluorescent surface15 in one dimension.

With a cathode ray tube of such construction, the diameter S of the spotof electron beams 22 on the fluorescent surface 15 may be expressed bythe following equation:

(Ql I o where:

P distance from the crossover point of electron beams to the air gapcenter of the focusing coil 24 Q distance from the air gap center of thefocusing coil to the fluorescent layer 15 of the target 16 S diameter ofthe electron beam spot at the crossover point 23. Generally, the cathoderay tube is demanded to have a high degree of resolution. To this end,the spot should have as small a diameter S as possible. Though it isonly required to reduce S in order to decrease S, the reduction of S issubject to limitation from the standpoint of preserving the propertiesof the cathode ray tube. A]- ternatively, therefore, there is adoptedthe process of limiting S to a certain value and instead increase PHowever, this generally results in an extremely elongated cathode raytube.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a cathode ray tube which is decreased in its entire lengthwithout lowering its resolution. According to one aspect of theinvention, there is provided a cathode ray tube wherein there isdisposed between the target and deflecting coil a dynamic focusingdevice comprising a pair of mutually intersecting focusing coils andthere is introduced through said focusing device current of saw toothwave having the'same frequency as that of the current supplied to thedeflecting coil to generate an electromagnetic field acting in the samedirection as that in which there are deflected electron beams, therebyreducing the spot of electron beams.

BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a sectional view of theconventional cathode ray tube;

FIG. 2 is a perspective view of a cathode ray tube according to anembodiment of the present invention;

FIG. 3 is a sectional view of FIG. 2;

FIG. 4 illustrates the wave form of current flowing through the dynamicfocusing coil included in FIG. 2; and

FIG. 5 is a vectorial chart showing the direction of an electromagneticfield generated in the dynamic focusing device.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 2 and 3, theenvelope 30 assumes a funnel shape and consists of a conical or frontportion 31 and neck or rear portion 32. At the front part of the conicalportion 31 of the envelope 30 is disposed a target 33, which is formedof a fiber plate 34 prepared from a large number of optical fibersarranged in the same direction and a fluorescent layer 35 formed on theinside of said plate 34. Said fluorescent layer 35 has a metal backing35a mounted on the inside. In the neck portion 32 is received anelectron gun 36, which comprises a cathode electrode 38 for emittingelectron beams 37 toward the target 16 and first, second grid and anodeelectrodes 39, 40 and 41 arranged in turn toward the target 16 coaxiallywith the cathode electrode 38. On the inner wall of the conical portion31 is deposited a metal coating 31a as a final anode. On the outerperiphery of the cathode ray tube near the boundary between the conicalportion 31 and neck portion 32 is provided a deflecting coil 42 fordeflecting electron beams 37 through an angle 0. At that part of theouter periphery of the conical portion 31 which is defined between thedeflecting coil 42 and target 33 is set a dynamic focusing device 43,which consists of a pair of focusing coils 44 and 45 intersecting eachother at the same angle 6 as that through which there are deflectedelectron beams 37. The axis L-L of the focusing coil 44 intersects atright angles the electron beams 370 which are deflected toward the leftside of the fluorescent layer 35 to generate an electromagnetic fieldacting in the same direction as that in which the electron beams 37atravel. 0n the other hand, the axis R-R of the focusing coil 45intersects at right angles the electron beams 37b deflected to the rightside of the fluorescent layer 35 to generate an electromagnetic fieldwhich acts in the same direction as that in which the electron beams 37bare conducted (FIG. 3). Through the focusing coils 44 and 45 of thedynamic focusing device 42 is introduced current of saw tooth wavehaving the same frequency as that of the current flowing through thedeflecting coil 42. Through the focusing coil 44 runs current 46 of sawtooth wave shown in solid line in FIG. 4, and through the focusing coil45 flows current 47 having the same polarity as the current 46 and a sawtooth wave symmetrical with that of the current 46 as indicated inbroken line in FIG. 4, these two currents being introducedsynchronizingly with the electron beam deflecting current. When electronbeams 37 are deflected to the left side of the fluorescent layer 35,that is, assume the position of 37a, the focusing coil 44 is suppliedwith maximum saw tooth current 46 indicated at point tl in FIG. 4. Inthe focusing coil 45, the saw tooth current 47 has zero value, that is,no current flows therethrough. Under such condition, there is onlygenerated an electromagnetic field in the focusing coil 44. Saidelectromagnetic field is produced, as indicated by the arrow 48 of FIG.A, in the same direction as that in which the electron beams 37a aredeflected. When the electron beams are brought to the center of thedeflection range, the focus ing coils 44 and 45 receive current of anequal magnitude shown in FIG. 4, thereby creating electromagnetic fieldsacting in the directions denoted by the arrows 49 and 50 of FIG. 58respectively. The resulting composite electromagnetic field isgenerated, as indicated by the arrow 51, in the same direction as thatin which the electron beams 37 are deflected toward the center of thedeflection range. Conversely where the electron beams 37 are deflectedto the right side of the fluorescent layer 35, that is, assume theposition of 37b, there flows no current through the focusing coil 44 asindicated at point tr in FIG. 4, whereas the focusing coil 45 issupplied with maximum saw tooth current 47. In the focusing coil 45alone, therefore, is produced an electromagnetic field acting in thesame direction indicated by the arrow 52 of FIG. 5C as that in which theelectron beams 37b are deflected.

The foregoing description relates to the cases where the electron beams37 are deflected to the left, right and center of the fluorescent layer35. Even where the electron beams 37 are deflected in other directions,the aforementioned dynamic focusing device 43 always generates acomposite electromagnetic field acting in the same direction as that inwhich said electron beams 37 are deflected.

Thus the electron beams 37 emitted from the cathode electrode 38 passthrough the opening of the first grid electrode 39, are temporarilyfocused at crossover point 53, scattered, deflected by the deflectingcoil 42, again focused by the dynamic focusing device 43 and finallyimpinge on the fluorescent layer 35. Thus the electron beams 37 linearlyscan the fluorescent layer 35 in one dimension. The distance Q betweenthe target 33 and the intersection of the paired focusing coils 44 and45 of the dynamic focusing device 43 is far shorter than the distance Qbetween the target to of the conventional cathode ray tube and focusingcoil 23. The shortened Q realizes a prominent elevation of resolution.Further based on the same degree of resolution as in the prior art, thedistance P between the crossover point 53 and the intersection of thepaired focusing coils 44 and 45 of the dynamic focusing device 43 isalso shortened in proportion to Q to reduce the entire length of acathode ray tube.

In the aforementioned embodiments, the intersecting angle of the pairedfocusing coils 44 and 45 is chosen to be equal to the deflection angle 0of electron beams. However, this is not always necessary. The point isthat current be introduced in such a manner that a composite of theelectromagnetic fields generated by the focusing coils 44 and 45 acts inthe same direction as that in which the electron beams 37 are deflected.Further, the saw tooth current supplied to the focusing coils 44 and 45may have a wave form variable with the construction of a cathode raytube used.

In the above-mentioned embodiments there was described a cathode raytube including an optical fiber plate for scanning the target 33 in onedimension. However, the present invention is applicable to any othertypes of cathode ray tubes for one-or two-dimensional scanning. Further,the invention may be used not only in an electromagnetic deflectioncathode ray tube, but also in a static deflection type.

What we claim is:

l. A cathode ray tube comprising:

an envelope including a front portion and a neck portion;

a target disposed in the forward end of the front portion;

an electron gun positioned in the neck portion so as to emit electronbeams toward the target;

electron beam deflecting means placed on the envelope; and

a dynamic focusing device comprising a pair of mutually intersectingfocusing coils, said focusing device being interposed between the targetand deflecting means so as to generate an electromagnetic field actingin substantially the same direction as that in which the electron beamsare deflected, thereby focusing said electron beams.

2. The cathode ray tube according to claim 1 wherein the pairedfocusingcoils intersect each other at the same angle as the maximum deflectionangle of electron beams.

3. The cathode ray tube according to claim 2 wherein the paired focusingcoils are supplied with saw tooth currents respectively which have thesame polarity and mutually symmetrical wave forms.

4. The cathode ray tube according to claim 3 wherein the target includesa fiber plate prepared from a large number of optical fibers arranged inthe same direction and a fluorescent layer mounted on one side of saidplate.

5. The cathode ray tube according to claim 4 wherein the fluorescentlayer is provided with a metal backing.

l060l l 0624

1. A cathode ray tube comprising: an envelope including a front portionand a neck portion; a target disposed in the forward end of the frontportion; an electron gun positioned in the neck portion so as to emitelectron beams toward the target; electron beam deflecting means placedon the envelope; and a dynamic focusing device comprising a pair ofmutually intersecting focusIng coils, said focusing device beinginterposed between the target and deflecting means so as to generate anelectromagnetic field acting in substantially the same direction as thatin which the electron beams are deflected, thereby focusing saidelectron beams.
 2. The cathode ray tube according to claim 1 wherein thepaired focusing coils intersect each other at the same angle as themaximum deflection angle of electron beams.
 3. The cathode ray tubeaccording to claim 2 wherein the paired focusing coils are supplied withsaw tooth currents respectively which have the same polarity andmutually symmetrical wave forms.
 4. The cathode ray tube according toclaim 1 wherein the target includes a fiber plate prepared from a largenumber of optical fibers arranged in the same direction and afluorescent layer mounted on one side of said plate.
 5. The cathode raytube according to claim 4 wherein the fluorescent layer is provided witha metal backing.